A fuel cell is a device for generating power that converts chemical energy from a fuel and oxidant directly into electrical energy. It has such advantages as higher efficiency, less pollution and lower noise. A fuel cell may be a single fuel cell, or a fuel cell stack composed of a plurality of single fuel cells.
A single fuel cell generally comprises a proton exchange membrane (PEM) 1, an anode 2, a cathode 3 and a conductive polar plate 4, as shown in FIG. 1.
The PEM 1 is a non-waterproof and gasproof type of semi-permeable membrane that water may permeate through and gas may not permeate through, and has the property of proton conductivity. Furthermore, PEM 1 can prevent the explosion of fuel and oxidant due to their mixing.
The anode 2 is an electrode for gas diffusion. Its supporting material generally comprise conductive carbon fiber or carbon fabric. A catalyst for catalyzing the anode reaction is provided between the anode 2 and PEM 1. The anode catalyst typically includes platinum powder, platinum alloy powder, platinum powder carried on a carrier or platinum alloy powder carried on a carrier. The platinum alloy may contain platinum and at least one selected from the group consisting of ruthenium, tin, iridium, osmium and rhenium. The carrier is conductive and has a higher specific surface area, such as active carbon.
The cathode 3 is also an electrode for gas diffusion. Its constitution is similar to that of the anode, except that a catalyst provided between the cathode 3 and PEM 1 is used for catalyzing the cathode reaction. The cathode catalyst typically includes platinum powder and platinum powder carried on a carrier.
The conductive polar plate 4 is provided on the outside of anode 2 and cathode 3, and may be made from graphite or metal.
In a fuel cell, the oxidant generally may be air or oxygen, and the fuel may be hydrogen, methanol or ethanol, etc. For example, in the case of the fuel cell using methanol as fuel and air as oxidant, the following reactions take place during their electrochemical reaction:Anode CH3OH+H2O→CO2+6H++6e  (1)Cathode 3/2O2+6H++6e→3H2O  (2)
The following overall reaction can be obtained from the above reactions on the anode and cathode:CH3OH+3/2O2→CO2+2H2O  (3)
A potential difference between the anode 2 and the cathode 3 is generated by the electrochemical reaction between these two electrodes. Electrons generated from the anode 2 are captured by the cathode 3 through the conductive polar plate 4 located on the outside of the anode 2 and external conductive body, while protons generated from the anode 2 are transferred directly to the cathode 3 through PEM 1, so that this allows current generation. The voltage resulted from a single fuel cell during a normal operation is within the range from 0.3V to 1.0V. In practical applications, single fuel cells are usually connected in series to form a fuel cell stack in order to provide a higher voltage and power.
A flow-field plate is one of key parts in a fuel cell because the flow state of reactants and resultants in flow field depends on the structure of flow-field plate in a fuel cell. To sufficiently and uniformly provide reactants to electrodes and discharge reaction resultants in time is very important to ensure a normal operation of a fuel cell. Therefore, if reactants could not distribute uniformly on electrodes, reaction on electrodes would be heterogeneous. This will make a fuel cell local overheated due to the resulted heterogeneous distribution of current density, and then lower the fuel cell performances and shorten its service life. Furthermore, water generated from reaction would accumulate on the cathode with reaction going on if it could not be discharged in time. This will result that (1) reactants are difficult to contact with the catalyst due to the presence of water around the catalyst, i.e. “water-submerged electrode”, which directly influences fuel cell performances; (2) material transferring resistance for reactants across diffusion layer to catalysis layer is increased, which decreases the output power of a fuel cell; (3) parts of PEM will expand occasionally due to water accumulation.
CN1405909A disclosed a flow-field plate of fuel cell. As shown in FIG. 2, although a plurality of flow grooves extending parallel were formed on the flow-field plate to solve problems on reactants distribution and resultants discharge, its effects were not satisfied and some of problems still exist.